1. Field of the Invention
The present invention relates to a method and apparatus for lifting successive rings of corrugated steel panels to construct cylindrical grain bins.
2. Background of the Invention
Modern grain bins typically have cylindrical steel walls and conical steel roofs assembled from prefabricated components. The cylindrical steel wall of a modern grain bin is fashioned from curved steel panels having horizontal corrugations. Bolt holes are located about the edges of the curved steel panels so that panels can be fastened to the lower edge of an assembled roof and to each other in successive rings to complete a bin. Accordingly, the present method for assembling a grain bin generally includes the following steps: (a) laying a concrete foundation, (b) constructing a circular roof, (c) lifting the roof, (c) attaching a first ring of panels, (d) raising the roof and the first ring of panels, (e) attaching a second ring of panels to the first ring, and (f) attaching successive rings of panels to complete the bin.
Although the process for building a grain bin may seem simple, building a grain bin using present methods is really quite difficult and labor intensive. The most difficult part of bin construction is raising the successive circular rings of panels so that all parts of the structure stay level and lift at the same rate. If this is not done properly, parts of the structure will be overloaded and will fail. One bin raising method is to attach a pattern of jacks around the wall of the grain bin and carefully operate those jacks to incrementally raise each portion of the grain bin wall. In order to not overstress the wall panels, all the jacks must be operated in small increments or simultaneously. Such incremental operations or simultaneous manual operations require significant labor. Another method for lifting a grain bin includes the use of an overhead crane. This method is difficult because a single point suspension of a large grain bin is inherently unstable. A multi-point suspension of a large grain bin is subject to the same difficulties as a multi-point jacking operation.
The difficulty encountered by those constructing grain bins is further aggravated by the continuing shortage of labor in rural areas. In the United States, at the beginning of the twentieth century, large numbers of workers could be found in rural areas. Today, at the beginning of the twenty first century, rural areas in the United States are depleted of labor and increasing levels of mechanization and even automation are evident in farming operations and related activities. Still further, an increasing demand for grain bins is evident in rural areas because increasingly larger, mechanized farming operations have opted to rely on their own storage facilities as a way to cope with fluctuations in grain prices. Consequently, there has been a long felt and now an urgent need for a grain bin lifting system that will permit operators to construct a grain bin with a minimum of labor.
The bin lifting system of the present invention satisfies this long felt need by providing a safe and reliable way to raise a grain bin with significantly less labor. The bin lifting system includes identical positive displacement pumps, a power source for driving the pumps, a reservoir for storing hydraulic fluid, hydraulic cylinder actuated jacks that attach to and lift the bin structure, control valves for controlling the flow of hydraulic fluid between the pumps, the jacks and the reservoir and hydraulic lines for conveying hydraulic fluid between the pumps, the jacks and the reservoir. The hydraulic cylinders for actuating the jacks include an upper chamber and a lower chamber. A sliding piston separates the upper and lower chambers. The piston carries a piston rod that extends up through the hydraulic cylinder. The hydraulic pumps are driven by the power source at the same rate so that they each provide equal volumes of hydraulic fluid to one of the control valves. The control valves are used to control the movements of sets of jacks having at least one jack or as many as sixteen jacks. When controlling one jack, each one of the control valves can be moved between three positions: (a) a first, neutral position where the valve directs fluid from a pump back toward the reservoir, (b) a second, lift position where the valve directs fluid from the pump toward the lower chamber of the hydraulic cylinder and also directs fluid from the upper chamber of the hydraulic cylinder toward the reservoir to cause the piston and piston rod to rise and (c) a third, descent position where the valve directs fluid from the pump toward the upper chamber of the hydraulic cylinder and also directs fluid from the lower chamber of the hydraulic cylinder toward the reservoir to cause the piston and piston rod to lower. By using line splitters, each control valve can be connected a set of jacks having more than one jack as long as all the sets have equal numbers of jacks. To allow simultaneous operation of all of the sets of jacks, the control valves can be mechanically interconnected so that they all can be moved in unison. This results in a hydraulic system having a number of separate circuits that can be controlled as one unit by one operator who can now raise or even lower a large number of jacks in unison.
The jacks used in the present invention are substantially identical and include a series of successive telescoping masts. The series of successive telescoping masts includes a first mast, at least one next mast and a base mast. The first mast has a fixed member that engages the piston rod of the hydraulic cylinder as well as a bracket for attachment to the structure being lifted. The next mast has members for holding a removable bracket. Like the fixed member of the first mast, the removable bracket engages the piston rod of the hydraulic cylinder. The base mast is supported by legs and holds the hydraulic cylinder in place. All of the masts except the base mast have holes that receive pins so that when pinned they can be secured in an extended position.
Each jack is capable of lifting a structure by a distance greater than the stroke distance of its hydraulic cylinder because its telescoping masts can be lifted and secured successively. First, the first mast is attached to the structure by its bracket. After the first mast is lifted by the extending hydraulic piston, it is secured by a pin in relation to the next mast. The piston is retracted, and the removable bracket is placed on the next mast so that it can be lifted and secured by a pin. Each successive mast is then lifted so that the structure can be lifted by a distance much greater than the stroke of the hydraulic cylinder. The jacks raise the structure uniformly because the hydraulic pumps supply equal volumes of hydraulic fluid to the control valves and the identical hydraulic cylinders of each jack. A reverse lowering operation can be accomplished by sending hydraulic fluid to the upper chambers of the hydraulic cylinders and successively retracting the pistons and the masts. If needle valves are placed in the hydraulic lines leading to the lower chambers of each hydraulic cylinder, then fluid leaving the lower chambers of the hydraulic cylinders in a descent operation can be restricted and controlled thereby preventing the structure from descending too rapidly. When jacks of the present invention are used in combination with the above described hydraulic system, a large structure comprised of relatively wide panels can be raised by employing a series of simple, repetitive steps.